Yeast Starter Gravity Calculation

Been brewing for quite some time now, but realized i have never added my starter gravity to my wort OG. Looked online for some calculators but really didnt see any that could help. So my question is: If i make a 2L starter with a gravity of 1.040 (or less), how would I add that to my gravity reading of 6.5 gal. of wort @ 1.070? Also, is it as simple as taking a gravity reading after pitching and aerating? I always thought the suspended yeast and bubbles would effect the measurement. Any tips would be great thanks!

Its not really going to make that big of a difference. If you wanted to do the calculation, you'd have to figure out the points given by the starter and add that to the points given by the wort. For instance, if we assume that 2L is close enough to 2quarts, that gives you half a gallon of 1.040 wort which would give you 0.5 * 40 = 20points. In the full batch, you've got 6.5gal of 1.070 wort, or 6.5 * 70 = 455 points. If you added the two together, you'd now have a total of 475 points in 7 gal of beer, giving you a gravity of 1.068. I don't know about you, but I have a hard enough time with either my hydrometer or refractometer getting good measurements down to the .002, so my measurements probably contain enough uncertainty to make the adjustment unnecessary.

As for the rest, yeast shouldn't change the gravity since they're in suspension. The air might change it a little bit, but I doubt it would be enough to notice, unless its aerated enough to start getting bubbles on the hydrometer (like with CO2 after fermentation is done). I generally measure before I pitch the yeast, but that's just because its easier for me to grab some out of the BK than out of the carboy.

Assuming you are pitching the entire starter, add 200grams of DME and 2L of water to your recipe and use a recipe calculator to determine the estimated OG of the batch including the starter.

It ends up not making much difference from what you originally anticipated without the starter. Like .001 or .002.

If you take a hydrometer reading after pitching, the gravity will be different from the calculation above because the starter's gravity isn't 1.040 anymore. Some of it fermented.

So how do you determine the SG and FG of a starter? Is it based on OG for the batch you are working on or is there a basic starting grav for starters in general? Sorry didn't mean to jack the OP.

Wheelchair Bob

Rbeckett said:

So how do you determine the SG and FG of a starter? Is it based on OG for the batch you are working on or is there a basic starting grav for starters in general? Sorry didn't mean to jack the OP.

Wheelchair Bob

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Since the idea of a starter is to grow yeast, the OG should be 1.035-1.040 or so.

The FG should be 1.010-1.012ish depending on the brand and type of extract used (I do wort starters often, and they finish at 1.010). Most people don't check the FG of a starter, and just decant it off of the spent wort if it's a large one.